The invention relates to an optoelectronic device for detecting markings provided with contrasting patterns, comprising: a transmitter for emitting transmitting light rays, a receiver for receiving light rays, a deflection unit positioned for periodically reflecting the transmitting light rays across a monitoring range and for reflecting receiving light rays that are reflected by the markings, and an evaluation unit for evaluating the receiving signals present at the receiver output.
An optoelectronic device of this type is disclosed in German Patent Document DE 198 44 238 A1. This optoelectronic device is used to detect markings, in particular in the form of barcodes. The optoelectronic device comprises a transmitter that is followed by a transmitting optic and a receiver that is preceded by a receiving optic. The transmitting light rays emitted by the transmitter and the receiving light rays reflected by the markings are guided over a deflection unit. The deflection unit consists of a rotating polygonal mirror wheel with a predetermined number of mirror surfaces. With the aid of the deflection unit, the transmitting light rays are periodically guided over a monitoring range.
Diverse reflecting mirrors across which the transmitting light rays and the receiving light rays are guided are arranged between the transmitter and the deflection unit as well as between the receiver and the deflection unit. The transmitting light rays and the receiving light rays are respectively guided over the same mirror surface of the polygonal mirror wheel.
The optoelectronic device thus has a plurality of optical components across which the transmitting light rays and the receiving light rays must be guided.
The individual components, particularly the reflecting mirrors, must be suitably adjusted, which results in an undesirably high assembly expenditure during the manufacture of the optoelectronic device. The optoelectronic device furthermore has an undesirably large structural shape, particularly since a large amount of space is required for arranging the reflecting mirrors and the receiving optic in front of the receiver.
A particular disadvantage in this connection is the large gap necessary between the receiving optic and the deflection unit as a result of the predetermined focal length of the receiving optic.
A further and essential disadvantage of optoelectronic devices of this type is that an undesirably high share of parasitic and extraneous light rays unavoidably impinge on the receiver as a result of the large surface area of the receiving optic, thus reducing the detection safety of the optoelectronic device.
A different optoelectronic device of the type first mentioned above is known from International Publication WO 00/16 239 and is used for detecting barcodes. With this optoelectronic device, the transmitter and the receiver are arranged one above the other and at a distance to each other. The transmitting light rays emitted by the transmitter and the receiving light rays reflected back by the markings are guided across a deflection unit. The deflection unit is a polygonal mirror wheel with a predetermined number of mirror surfaces. The transmitting light rays and the receiving light rays are respectively guided over the same mirror surface of the polygonal mirror wheel. The transmitting light rays and the receiving light rays guided so as to be spatially separated. Thus, the transmitting light rays impinge on the upper partial segment of the respective mirror surface of the polygonal mirror wheel while the receiving light rays are guided over the lower partial segment of the same mirror surface.
The partial segments of the mirror surface where the transmitting light rays and the receiving light rays impinge must be clearly offset against each other to obtain a spatial separation between the transmitting light rays and the receiving light rays.
To achieve the desired spatial separation between the transmitting light rays and the receiving light rays, the height of the polygonal mirror wheel must be increased noticeably as compared to traditional polygonal mirror wheels. In turn, this requires an undesirable enlargement of the structural shape of the optoelectronic device.
It is therefore an object of the invention to provide an optoelectronic device of the aforementioned type in such a way that the highest possible detection safety is ensured with the smallest possible structural shape.
The above and other objects are accomplished by the invention by the provision of an optoelectronic device for detecting markings provided with contrasting patterns, comprising: a transmitter for emitting transmitting light rays; a receiver for receiving light rays, the receiver having an optical axis; a deflection unit positioned for periodically reflecting the transmitting light rays across a monitoring range and for reflecting receiving light rays that are reflected by the markings; an evaluation unit for evaluating the receiving signals present at the receiver output; and a light-impermeable insert within which the receiver is positioned, the insert including channel structures extending in a direction of the optical axis for the receiver, for guiding the receiving light rays reflected by the deflection unit to the receiver.
One essential advantage of the invention is that the receiver inside the insert is located directly opposite the deflection unit without a receiving optic and reflecting mirrors positioned in-between. As a result, the distance between receiver and deflection unit can be kept very short, which results in a corresponding reduction in the structural size of the optoelectronic device. The number of optical components of the optoelectronic device is consequently also reduced considerably, so that the device can be produced easily and at low cost.
Another essential advantage of the optoelectronic device according to the invention is that the parasitic and extraneous light rays impinging on the receiver are reduced considerably as a result of the guidance of the receiving light inside the channel structures of the insert. In turn, this leads to a high detection safety for the optoelectronic device.
This reduction is based on the fact that the geometry of the insert is adapted optimally to the guidance of the receiving light rays because the channels of the channel structures extend parallel to the optical receiver axis. The receiving light rays traveling along the optical axis therefore impinge almost without obstruction on the receiver. In contrast, parasitic and extraneous light rays that impinge at an angle hit the light-impermeable wall elements of the channel structures and thus can no longer hit the receiver.
For an optimum blocking of the parasitic and extraneous light rays, the channel structures are designed to be as long as possible and to extend right up to the deflection unit. The channel structures additionally form a honeycomb-type pattern, consisting of several channels for which the diameters are considerably smaller than the lengths. As a result, it is ensured that even parasitic and extraneous light rays arriving at very small angles to the optical axis of the receiver hit the wall elements of the channel structures and not the receiver.
According to one advantageous embodiment, the wall elements of the channel structures are roughened up or further structured, thus functioning as light traps for the parasitic and extraneous light rays. That is to say, the rays are prevented from finally reaching the receiver following multiple reflections on the wall elements.
According to one exemplary modification of the invention, the insert can consist of a conductive material, thus providing the receiver with additional EMC (electromagnetic compatibility) protection.
In a further exemplary embodiment of the invention, the transmitting light rays and the receiving light rays extend coaxially. For this, the transmitter is also arranged inside the insert and is positioned directly behind the receiver. The transmitting light rays are guided through a recess in the light-sensitive surface of the receiver. As a result, the transmitting light rays are at least partially enclosed by the light-sensitive surface.
The transmitting light rays and the receiving light rays for this embodiment are guided inside separate channels of the channel structure, thus resulting in a nearly complete separation of the transmitting light rays from the receiving light rays.
The aforementioned embodiment furthermore has an especially compact design.